专业英语9-10说课讲解.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,*,Lesson 12Bituminous Surface Courses,The bituminous surface course has to provide,resistance,(抵抗),to the effects of repeated loading by,tyres,（轮胎）,and to the effects of the environment.,In addition,it must offer adequate,skid resistance,（抗滑能力）,in wet weather as well as comfortable vehicle ride.It must also be resistant to,rutting,（车辙）,and to,cracking,（裂缝）.,It is also desirable that surface course is,impermeable,（不渗水的）,except in the case of,porous asphalt,(多空隙沥青面层).,Hot rolled asphalt(HRA),（热压沥青混凝土）,is a,gap graded,（间断级配）,material with less,coarse aggregate,（粗集料）.,In fact it is essentially a bitumen/,fine aggregate,（,细集料）,/,filler,（填料）,mortar,（胶浆）,into which some coarse aggregate is placed.,The mechanical properties are dominated by those,of the mortar.This material has been extensively,used as the wearing course on major road in the,UK,though its use has recently declined as new,materials have been introduced.,It provides a,durable,（耐久的、耐用的,）layer with good resistance to cracking and one which is relatively easy to,compact,（压实）.,The coarse aggregate content is low(typically 30%)which results in the compacted mixture having a smooth surface.,Accordingly,（因此）,the skid resistance is inadequate and,precoated,（预浇）,chippings,（石屑）,are rolled into the surface at the time of laying to correct this,deficiency,（不足）.,In Scotland,HRA wearing course remains the preferred wearing course on trunk roads,（干线道路）,including,motorway,（高速公路、汽车专用公路）,butsince 1999 thin surfacings have been the preferred option in England and Wales.Since 1999 in Northern Ireland,HRA wearing course and thin surfacings are the preferred permitted options.,Porous asphalt(PA)is a,uniformly graded,（单一级配）,material which is designed to provide large,air voids,（空隙率）,so that water can drain to the,verges,（路肩、边缘）,within the layer thickness.If the wearing course is to be effective,the,basecourse,（基层）,below must be,waterproof,（防水的）,and the PA must have the ability to retain its open,textured,（构造、纹理）,properties with time.,Thick,binder films,（吸附沥青膜）,are required to resist,water damage,（水损害）,and,ageing,（老化）,of the binder.In use,this material minimizes vehicle,spray,（水雾）,provides a quiet ride and lower rolling resistance to traffic than,dense mixtures,（密级配混合料）.,Bituminous Surface Courses,It is often specified,（指定）,for environmental reasons but,stone mastic asphalt,(SMA),(沥青玛蹄脂碎石),and specially thin surfacings are generally favoured in current UK practice.,There have been high profile instances where a PA wearing course has failed early in its life.The,Highways Agency,（公路局）,does not recommend the use of a PA at traffic levels above 6000,commercial vehicles,（载重车）,per day.,Asphaltic concrete,（沥青混凝土）and,dense bitumen macadam,(DBM)（密级配沥青碎石）are,continuously graded mixtures,（连续级配混合料）similar in principle to the DBMs used in,roadbases,(基层)and basecourses but with smaller,maximum particle sizes,（最大粒径）.,Asphaltic concrete tends to have a,slightly,（稍微）,denser grading and is used for road surfaces throughout the world with the excepting of the UK.,It is more difficult to meet UK,skid resistance Standards,（抗滑标准）,with DBMs than HRA,SMA or PA.This problem can be resolves by providing a separate surface treatment but doing so generally makes DBM economically unattractive.,Stone mastic asphalt(SMA)material was,pioneered,（开辟、开路）,in Germany and Scandinavia and is now widely used in the UK.SMA has a coarse,aggregrate skeleton,（碎石骨架）,like PA,but the voids are filled with a fine aggregate/,filler,（填料）,/bitumen mortar.,In mixtures using,penetration grade bitumen,（石油沥青）fibres,（纤维）,are added to,hold,（吸收、吸附）,the bitumen within the mixture(to prevent“binder drainage”).,Bitumen,oil bitumen(earth oil),natural bitumen,Tar,Where a,polymer modified bitumen,（聚合物改性沥青）,is used,there is generally no need for fibres.SMA is a gap-graded material with good resistance to rutting and high,durability,（耐久性）.,modified bitumen,SBS,SBR,PEEVA,It differs from HRA in that the mortar is designed to just fill the voids in the coarse aggregate whereas,in HRA,coarse aggregate is introduced into the mortar and does not provide a continous,stone matrix,（矿质骨架）.,The higher stone content HRAs,however,are rather similar to SMA but are not wide used as wearing courses in the UK,being preferred for roadbase and basecourse construction.,A variety of thin and what were called,ultra,（超的、极端的）,thin surfacings(nowadays,the tendency is to use the term thin surfacings for both thin and ultra thin surfacings)have been introduced in recent years,principally as a result of development work concentrated,（集中）,in France.,These materials vary in their detailed,constituents,（成分、要素、组成部分）,but usually have an aggregate grading similar to SMA and often,incorporate,(联合、结合、加入),a polymer modified bitumenThey may be used over a high stiffness roadbase and basecourse or used for,resurfacing,（,翻修路面）,of existing pavements.For heavy duty pavements(i.e those designed to have a useful life of forty years),the maintenance,philosophy,（哲学、哲理）,is one of minimum lane,occupancy,（占用）,which only allows time forreplacement,（替换）,of the wearing course to these long life pavement structures.The new generation of thin surfacings allows this to be conveniently achieved.,The various,generic,（种类的）,mixture types described above can be compared with respect to their mechanical properties and durability characteristics by,reference,（参考）,to Fig.12.1.This shows,in principle,how low stone content HRA,asphaltic concrete,SMA and PA mixtures,mobilize resistance,(流动阻力),to loading by traffic.,Asphaltic concrete(Fig.12.1a)presents something of a,compromise,（和解、折衷方案）,when well designed,since the dense aggregate grading can offer good resistance to the,shear stresses,（剪切应力）,which cause rutting,while an adequate binder content will provide reasonable resistance to the,tensile stresses,（拉应力）,which cause cracking.,In general,the role of the aggregate dominates.DBMs tend to have less dense gradings and properties which,therefore,tend towards good rutting resistance and away from good crack resistance.,HRA(Fig.12.1b)offers particularly good resistance to cracking through the binder rich mortar between the coarse aggregate particles.This also provides good durability but the lack of coarse aggregate content,inhibits,（防止、制止）,resistance to rutting.,SMA and PA are shown in the same diagram(Fig.c)to emphasis the dominant role the coarse aggregate.In both case,well coated stone is used.In PA,the void space remains available for drainage of water,whilst in SMA,the space is occupied by a fine aggregate/filler/bitumen/fibre mortar.,Both materials offer good rutting resistance through the coarse aggregate content.The tensile strength of PA is low whilst that of SMA is probably adequate but little mechanical testing data have been reported to date.,Lesson 13,Drainage for Road and Airports,Provision of adequate,drainage,(,排水,),is important factor in the,location,（定位）,and,geometric,（几何学的、几何图形的）,design of road and airports.,Drainage facilities,(,排水设施,),on any highway,street and airport should adequately provide for the flow of water away from the surface of the pavement to properly designed channels.,Inadequate drainage will,eventually,(,最后、终于,),result in serious damage to the structure.,In addition,traffic may be slowed by,accumulated water,（积水）,on the pavement,and accidents may occur as a result of,hydroplaning,（水滑现象）,and loss of visibility from,splash,（喷溅）,and,spray,（喷洒、喷雾）,.,The importance of adequate drainage is recognized in the amount of highway construction dollars,allocated,(,分配、分派,),to drainage facilities.,About 25 percent of highway construction dollars,are spent for,erosion,（冲刷、侵蚀）,control and,drainage structures,such as,culverts,（涵洞）,bridges,channels,and,ditches,（明）沟、渠）,.,Highway Drainage Structures,（公路排水结构物）,One of the main concerns of the highway engineer is to provide an adequate size structure,such that the,waterway opening,（过水孔径）,is sufficiently large to,discharge,（放、排出）,the expected flow of water.,Inadequately sized structures can result in water,impounding,(,集水、蓄水,),which may lead to failure of the,adjacent,（邻近的）,sections of the highway due to,embankments,（路堤）,being,submerged,（浸没、浸入水中）,in water for long periods.,The two general categories of drainage structures are major and minor.,Major structures,（大型结构物）,are those with,clear spans,（净跨（径）,greater than 20 feet,whereas minor structures are those with clear spans of 20 feet or less.,Major structures are usually large bridges,although,multiple-span culverts,（多孔涵洞）,may also be included in this class.Minor structures include small bridges and culverts.,Emphasis is placed on selecting the span and vertical,clearance净空）,requirements for major structures.The bridge,deck,（桥面）,should be located above the,high water mark,（高水位线）,.,The clearance above the high water mark depends on whether the waterway is,navigable,（可通行的、可通航的）,.,混凝土连续箱梁,591-605,If the waterway is navigable,the clearance above the high water mark should allow the largest ship using the channel to pass,underneath,（在下面）,the bridge without,colliding with,(,碰撞,),the bridge deck.,The,clearance height,（净空高度）,type,and spacing of,piers,（桥墩）,also depend on the probability of,ice jams,（冰块拥塞）,and the,extent,（程度）,to which,floating logs,（漂浮的圆木）,and,debris,垃圾）,appear on the waterway during high water.,武汉长江大桥,An examination of the,banks,（堤（岸）,on either side of the waterway will indicate the location of the high water mark,since this is usually associated with signs of,erosion,（冲刷、侵蚀）,and debris,deposits,（沉淀物、沉积物）,.,Local residents,who have lived near and observed the waterway during,flood stages,（洪水期间）,over a number of years,can also give,reliable,（可靠的）,information on the location of the high water mark.,Stream gauges,（水文站）,that have been installed in the waterway for many years can also provide data that can be used to locate the high water mark.,Minor structures,consisting of short-span bridges and culverts,are the,predominant,（占优势的、主要的）,type of drainage structures on highways.Although openings for these structures are not designed to be adequate for the worst flood conditions,they should be large enough to,accommodate,（适应、容纳）,the flow conditions that might occur during the,normal life expectancy,（正常使用年限）,of the structure.,Provision should also be made for preventing,clogging,（障碍、阻塞）,of the structure due to floating debris and large,boulders,（圆石、巨砾）,rolling from the banks of steep channels.,Drainage for Road and Airports,Culverts are made of different materials and in different shapes.Materials used to construct culverts include concrete,（,reinforced and unreinforced,）,corrugated steel,（波纹钢筋）,and,corrugated,（波状的）,aluminum,（铝）,.,Other materials may also be used to,line,（衬里）,the,interior,（内部、里面）,of the culvert to prevent,corrosion,（腐蚀、锈蚀）,and,abrasion,（磨损、磨耗、磨蚀）,or to reduce hydraulic,（水力的、水压的）,resistance.,For example,asphaltic concrete may be used to line corrugated metal culverts.The different shapes normally used in culvert construction include circular,rectangular,（矩形的）,(box),elliptical,（椭圆形的）,pipe arch,metal box,and arch.,Municipal,（城市的、市政的）,Storm Drainage,In urban and suburban,（市郊的）,areas,runoff waters,（径流水）,are handled through a system of drainage structures referred to as,storm sewers,（雨水管）,and their,appurtenances,（附属物）,.,The drainage problem is increased in these areas primarily for two reasons:the,impervious,（不透水的）,nature of the area creates a very high runoff;and there is little room for natural,water courses,（水流）,.,It is often necessary to collect the entire storm water into a system of pipes and,transmit,（传送、转达）,it over considerable distances before it can be loosed again as surface runoff.This collection and transmission further increase the problem,since all of the water must be collected with virtually no,pending,（积水、积水库）,thus eliminating any natural storage;and through increased,velocity,（速度）,the peak runoffs,（最大流量）,are reached more quickly.,Also,the shorter times of,peaks,（峰、高峰）,cause the system to be more,sensitive,（灵敏的、敏感的）,to,short-duration,（持续时间短）,high intensive,（强烈的、密集的）,rainfall.Storm sewers,like culverts and bridges,are designed for storms of various,intensity-return-period,(,强度重现期,),relationships,depending upon the economy and amount of ponding,（积水）,that can be tolerated.,Airport Drainage,The problem of providing proper,drainage facilities,（排水设施）,for airports is similar in many ways to that of highways and streets.However,because of the large and relatively flat surface involved,the varying soil conditions,the absence of natural,water courses,（水道）,and possible,side ditches,（边沟）,and the greater concentration of,discharge,（流量、排出量）,at the,terminus,（终点、界限）,of the construction area,some phases of the problem are more complex.,For the average airport the over-all area to be drained is relatively large and an extensive drainage system is required.The,magnitude,（数量、等级）of such a system makes it even more,imperative,（强制的、不可避免的）,that,sound engineering principles,（可靠的工程原理）,based on all of the best available data be used to ensure the most economical design.,Overdesigning,（过于安全的设计）,of facilities results in excessive money investment with no return,and,underdesigning,欠安全的设计）,can result in conditions hazardous to the air traffic using the airport.,Drainage for Road and Airports,In order to ensure surfaces that are smooth,firm,（坚固）,stable,（稳定）,and reasonably free from flooding,it is necessary to provide a system which will do several things.It must collect and remove the surface water from the airport surfaces;,intercept,(,阻断、拦截,),and remove surface water flowing toward the airport from adjacent areas;collect and remove any excessive,subsurface water,（地下水）,beneath the surface of the airport facilities and in many cases lower the,ground-water table,（地下水位）,;,and provide protection against erosion of the sloping areas.,Lesson14Freeways,Freeways,especially those built to Interstate,（洲际的、洲间的）,standards are the safest of the various classes of highways.,While control of access,(出入),which limits vehicle conflicts,（车辆冲突）,is a primary factor in relatively low accident,injury,and fatality rates,（死亡率）,other design features,such as wide medians,（中央分隔带）,and shoulders,roadsides clear of obstructions,（路边无障碍物）,and the extensive use of protective barriers,（护栏）,are key factors as well.,Freeways,The higher design speeds used for freeways result in long sight distances due to long radius horizontal curves and long vertical curves,and other desirable design features that create a safe driving environment.Although most of the nations freeways enjoy this relatively high level of design and safety,there are many opportunities for further,enhancements,（加强、提高）.,Safety improvements on freeways can also result in substantial savings in,life and property,（生命和财产）,because freeways carry 25 percent of the nations total traffic.,Freeways,Selecting the design speed for a freeway is an important safety element because most,geometric criteria,（几何线形标准）,are related to or